Radio frequency anechoic chambers are used to provide controlled repeatable environments for performing radio frequency radiation tests. Radio frequency anechoic chambers are meant to approximate unbounded regions of free space for electromagnetic waves and are meant to provide environments in which radio frequency radiation tests can be made without introducing errors caused by reflected waves or standing waves.
One type of test performed in radio frequency anechoic chambers is the measurement of power radiated from a piece of radio frequency equipment (termed the Equipment Under Test, EUT) as a function of polar and azimuth angle. Such a test allows a complete characterization of the spatial dependence of electromagnetic waves radiated by the EUT. The floor, ceiling and walls of radio frequency anechoic chambers are tiled with radio frequency absorbers that are provided to substantially diminish reflections and standing waves. The EUT is supported away from the absorbing walls, ceiling and floor, in order to make measurements. Elevating the EUT with a support also allows a measurement antenna to be moved so as to view the EUT from a wide range (nearly 180 degrees) of polar angle. To avoid large disturbances of the radio frequency fields emitted by the EUT, the support is made from dielectric materials as opposed to metal. An improved test stand that is suitably used in anechoic chambers is covered in co-pending patent application Ser. No. 10/805996.
One measure of the quality of an anechoic chamber is the magnitude of unwanted reflections. In an ideal anechoic chamber, there are no reflections. One way to measure the level of unwanted reflections of radio frequency waves in an anechoic chamber that is configured for measuring radiated radio frequency wave power as a function of polar angle, is to install a transmitting antenna that radiates uniformly as a function of polar angle (e.g., a horizontally oriented dipole) at a center of rotation and rotate a receiving antenna over a large range of polar angle with respect to the transmitting antenna while measuring the power received by the receiving antenna. In an ideal radio frequency anechoic chamber there would be no variation in the measured field. The variation that occurs is termed “ripple”. Ripple can arise from a variety of sources.
Certain tests performed in anechoic chambers call for wireless communication to be maintained between the EUT and a test equipment transceiver. For example, to simulate real use, the power radiated from the EUT is suitably measured while the EUT is exchanging signals with a test equipment transceiver. In order for a test equipment transceiver to be able to communicate wirelessly with an EUT, an antenna that is connected to the test equipment transceiver is placed in the anechoic chamber. In certain commercial systems, a spiral antenna is placed in an anechoic chamber. Placing an additional antenna in an anechoic chamber has the drawback that the additional antenna will partly reflect signals emitted by the EUT, thereby increasing the ripple in the anechoic chamber. Thus, there is a desire to maintain a wireless link between an EUT and a test equipment transceiver without introducing an antenna that will cause substantial reflections and increase the amount of ripple.